Conventionally, there has been such a torque limiter as disclosed in Japanese Patent Publication No. JP-A-07-310753 (Patent Document 1).
This torque limiter is so constructed that an inner peripheral face of a tube member is fitted over an outer peripheral face of a shaft member, and by supplying pressurized oil to an oil pressure expanding chamber of the tube member, the inner peripheral face of the tube member is reduced in diameter by the pressurized oil in the oil pressure expanding chamber, and pressed against the outer peripheral face of the tube member. In this manner, the shaft member is frictionally coupled to the tube member thereby to transmit a torque. Then, the pressurized oil in the oil pressure expanding chamber is sealed with a shear tube, and a locking member locked to an end part of the shear tube is fixed to the shaft member.
When a rotary position of the shaft member with respect to the tube member is changed, because a load more than a determined value has been exerted on the shaft member or the tube member, and the inner peripheral face of the tube member has slipped with respect to the outer peripheral face of the shaft member, the end part of the shear tube is cut by the locking member, and the pressurized oil in the oil pressure expanding chamber is discharged to the exterior, through an oil removing hole which is formed in the shear tube. As the results, the inner peripheral face of the tube member becomes unable to be pressed against the outer peripheral face of the shaft member, and the frictional coupling between the shaft member and the tube member is released, thereby to interrupt transmission of the torque. Moreover, lubricating oil is applied between the shaft member and the tube member, for the purpose of preventing burn-outs of the shaft member and the tube member, which occurs when a load more than the determined value has been exerted on the shaft member or the tube member, and the inner peripheral face of the tube member is sliding with respect to the outer peripheral face of the shaft member.
In the above described conventional torque limiter, when a load more than the determined value has been exerted on the shaft member or the tube member, and the inner peripheral face of the tube member has slipped with respect to the outer peripheral face of the shaft member, the oil in the oil pressure expanding chamber must be rapidly removed. Otherwise, dynamic friction force is exerted on respective frictionally engaged faces of the shaft member and the tube member for a long time, and burn-outs are likely to occur on the frictionally engaged faces of the shaft member and the tube member.
For this reason, in the conventional or existing torque limiter, it is desired to remove the oil from the oil pressure expanding chamber more rapidly, thereby to shorten the time that the dynamic friction force is exerted on the shaft member and the tube member, when a load more than the determined value has been exerted on the shaft member or the tube member, and the inner peripheral face of the tube member has slipped with respect to the outer peripheral face of the shaft member.    Patent Document 1: Japanese Patent Publication No. JP-A-7-310753